1. Field of the Invention
The present invention relates to a crimping device and, more particularly, to a method and device for crimping a stented prosthetic valve such as a heart valve from a large diameter to a smaller diameter.
2. Description of the Related Art
A stent is a generally cylindrical prosthesis introduced into a lumen of a body vessel via a catheterization technique. Stents may be self-expanding or balloon expandable. Balloon-expandable stents are typically crimped from an initial large diameter to a smaller diameter prior to advancement to a treatment site in the body. Before crimping, a balloon expandable stent is typically placed over an expandable balloon on a catheter shaft. In cases where the stent was manufactured in its fully crimped diameter, the stent is expanded and then crimped on the balloon. To ensure safety, the crimping process should be performed in a sterile environment. Over the years, attempts have been made to crimp the stent on a balloon during the operation in the sterile field. However, most stents are now “pre-crimped” on a suitable balloon in the factory and then delivered to the physician ready for use.
One example of a crimping device based on movable segments is disclosed in U.S. Pat. No. 6,360,577 to Austin. This crimping device uses sloped planes which force jaws to move from the open position to the closed position. In one primary shortcoming associated with this type of device, the length of the sloped plane is given by a whole circle divided by the number of activated jaws. The more jaws for crimping means a shorter sloped plane for activating. The drawback of this method is the contradiction created by the equation of 360 degrees divided by the number of jaws. In order to achieve a smooth aperture for crimping the valve a large number of jaws is needed, but a long sloped plane is preferably to reduce circumferential resistance or friction forces. For example, a linear movement of 7 mm is achieved by a rotational movement of approximately 45 degrees (360 divided by 8 jaws), which is quite a steep slope angle that requires more turning force to overcome. Therefore, the effectiveness of this type of device is substantially limited.
In recent years, a variety of prosthetic valves have been developed wherein a valve structure is mounted on a stent and then delivered to a treatment site via a percutaneous catheterization technique. Prosthetic valves are typically much larger in diameter relative to coronary stents. For example, a typical coronary stent diameter is only 1.5 to 4.0 mm in its expanded size, while a stented prosthetic valve diameter will typically be in the range of about 19 to 29 mm, at least 5 times as large as a coronary stent. In another difference, coronary stents are stand-alone devices while, in prosthetic valves, the stent functions as a scaffold to hold the valve structure. The valve structure is typically made of biological materials such as pericardium valves or harvested valves. For improved function after deployment, it is often desirable to preserve such valves in the open (i.e., expanded) diameter inside a preserving solution. Using this procedure, it may be necessary to crimp the valve in the operation room a few minutes before implantation, therefore precluding pre-crimping by the manufacturer over a balloon.
Due to the unique crimping requirements for stent-based prosthetic valves, it has been found that existing crimping devices configured for use with coronary stents are not suitable for use with stent-based prosthetic valves. In addition, as discussed above, existing crimping mechanisms suffer from a variety of shortcomings which limit their ability to be adapted for use with stent-based prosthetic valves. Due to the deficiencies associated with existing crimping technology, a new crimping device was developed by Percutaneous Valve Technologies, Inc. (PVT) that is better suited for use with stent-based prosthetic valves. This crimping device is described in co-owned U.S. Pat. No. 6,730,118 to Spenser, et al. and relates to a crimping device that is adapted to crimp a prosthetic valve as part of the implantation procedure.
Another version of a prosthetic heart valve crimper is marketed by Machine Solutions Inc. of Flagstaff, Ariz. The HV200 is a disposable crimper that uses multiple pivoting segments to crimp percutaneous heart valves. The Machine Solutions crimpers are also disclosed in U.S. Pat. Nos. 6,629,350 and 6,925,847, both to Motsenbocker. These crimping devices are based on segments which rotate about pivot pins to create radial compression. Unfortunately, the pivoting design tends to concentrate stress in certain areas of the individual segments, and in the mechanism for pivoting them. Also, the user must apply significant force to close the crimper aperture around a relatively large percutaneous heart valve.
Although the heart valve crimping technology available to date provides an improvement over the existing stent crimper technology, it has been found that a need still exists for a more effective device. It is desirable that such a device be capable of crimping a valve from a diameter of about 29 mm to a crimped size of about 6 mm without requiring excessive force and without inducing high mechanical stresses within the device. It is also desirable that such a device is simple to use and relatively inexpensive to manufacture. It is also desirable that such a device be sterile and suitable for manual operation in a catheter lab or operating room. The present invention addresses this need.